Eiwaz or Eihaz is the reconstructed Proto-Germanic name of the rune ᛇ, coming from a word for "yew".
The latter is possibly an early loan from the Celtic, compare Gaulish ivos, Breton ivin, Welsh ywen, Old Irish ēo.
[1] Bengt Odenstedt suggests it may have been adapted from the classical Latin alphabet's Z,[2] or Y[citation needed].
The rune survives in the Anglo-Saxon futhorc as ᛇ Ēoh or Īh "yew" (note that ᛖ eoh "horse" has a short diphthong).
In futhorc inscriptions Ēoh appears as both a vowel around /iː/, and as a consonant around [x] and [ç].